(1) Field of the Invention
The invention relates to a method for recording pulse signals of an input channel of a microscope, in particular of a confocal microscope or a laser scanning microscope, where the channel is sampled at a predetermined sampling frequency for pulse signals.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The invention is preferably used for fluorescence correlation spectroscopy (FCS), and scanning fluorescence correlation spectroscopy (S-FCS), carried out by means of a laser scanning microscope (LSM). With FCS and S-FCS, individual fluorescence emissions are recorded with photon counting detectors, the response signal of which is digitized with a predetermined sampling frequency. The response signals are short pulse signals. The occurrence of a pulse signal is referred to as a pulse signal event. The temporal density of the events is low in this case. A Photomultiplier Tube (PMT) or Avalanche Photodiode (APD), can be used as a photon counting detector.
In the prior art, a method for recording pulse signals of two input channels for FCS are known from U.S. Pat. No. 6,591,223, for example, the disclosure of which is incorporated by reference herein as if reproduced in full. In a first embodiment, after the detection of an event in at least one of the input channels or after overflow of a counter, the current state of all input channels together with a magnitude that characterizes the time interval to the last storage are stored. In a second embodiment, after the detection of an event in at least one of the input channels or after overflow of a counter, the states of all input channels in the scanning cycle in which the event has occurred, and for a specified number of scanning cycles after the occurrence of the first event together with a magnitude that characterizes the time interval to the last preceding storage, are stored.
Due to the storing scheme of the states of all input channels, this type of recording has disadvantages in that the absolute times at which the individual events have occurred cannot be reconstructed and that the number of input channels which can be used simultaneously is basically limited by the width of the memory registers in which the digitized input channels are mapped.